What is a Marine Chronometer?
A Marine Chronometer is a watch with an accuracy high enough (what this means, you will see later) to determine the longitude of a position on land and more importantly on sea. To get a general overview of what a Marine Chronometer is you can check out Wikipedia:
Accuracy of a Marine Chronometer
There is not much written about the minimum requirements of a Marine Chronometer. As a rule of thumb we can say that a Marine Chronometer should not loose or win more than 2 seconds per month. Also important, accuracy must be granted under all sorts of different conditions as temperatures or shocks. With this rule we can state that a Marine Chronometer is within +/- 24 Seconds per year. To give you a comparison, a normal quartz watch is within +/-30 seconds/month and a good mechanical wristwatch on the other hand is within 90 seconds/month.
Reasonable Accuracy Expectations
by Type of Watch |
Seconds gain/loss per day |
Best
Accuracy |
Worst |
Typical |
Best |
Vintage mechanical watch
in good repair |
+/-60 |
+/-15 |
+/-5 |
99.9826% |
Modern mechanical watch
non-certified |
+/-10 |
+/-5 |
+/-2 |
99.9942% |
Modern mechanical watch
chronometer certified |
+6/-4 |
+/-3 |
+/-1 |
99.9977% |
Modern quartz watch
non-certified (normal) |
+/-2 |
+/-1 |
+/-0.1 |
99.9998% |
Modern quartz watch
marine chronometer quality |
+/-0.02 |
+/-0.02 |
+/-0.0 |
99.9999% |
Source: http://www.chronocentric.com/watches/accuracy.shtml
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